Disk Partitioning
By: Stefano Polo
Overview
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Creating divisions on a Hard Disk
Directories and files are then
grouped by categories
• Data types
• Usage
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Partitions contains file systems
• Space Management
• Access Permissions
• Directory Searching
Overview cont.
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A file system can decide how many
separate categories of data are
needed and the size of each.
• Seperating operating system from user
files
Examples
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Partition for Swapping
• Keeps frequently used programs and
data near each other
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Keeping browser cache files in
separate partitions keeps them away
from each other
Seperating email from audio and
photos
Benefits
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The Use of Multi-booting setups
• Having more than 1 operating system
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Sharing swap partitions between multiple linux
distributions
• Allows the need for less memory
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Protecting and isolating files
• Easy to recover corrupted file systems and operating
systems installed
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Increase Computer performance
• Smaller file systems are more efficient
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Higher level of data organization
• Keeping videos, photos, audios, emails, etc…seperated
PC Bios Partition Types
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Used in MS-Dos, Windows, & Linux
Can contain up to 4 Primary or 1-3
primary and 1 extended
Each partition have 16-byte entries
in the partition table located in the
Master Boot Record
A primary partition contains one file
system
Primary (Logical)
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The "partition type" code for a primary or logical
partition can either correspond to a file system
contained within (e.g. 0x07 means either an
NTFS or an OS/2 HPFS file system) or indicate
the partition has a special use (e.g. code 0xBC
may mean an Acronis Secure Zone and code
0x82 usually indicates a Linux swap partition).
The FAT16 and FAT32 file systems have made use
of quite a number of partition type codes over
time due to the limits of various DOS and
Windows OS versions. Though a Linux operating
system may recognize a number of different file
systems (ext2, ext3, reiserfs, etc.), they have all
consistently used the same partition type code:
0x83 (Linux native). (wikipedia)
NTFS
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All file data are stored as metadata
• Simply just data about data
• May describe individual datum, content item,
or a collection of data
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Allows any sequence of 16-bit values for
name encoding
uses B+ trees to index file system data
Master File Table (MFT) contains metadata
about every file, directory, and metafile on
an NTFS volume
File Allocation Table (FAT)
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Used mostly today in floppies and solid-state memory cards
(flash memory)
Gives convenience towards sharing data between operating
systems on one machine
Uses a table which contains information on which areas that
belong to files are free or unusable
Table also gives information on where the data is actually
stored
To limit the size of the table, disk space is allocated in
hardware sectors called clusters
Maximum numbers of clusters have increased over time
the number of bits required to identify a cluster is used to
name the successive major versions of the format
• Fat12
• Fat16
• Fat32
Drawbacks of FAT
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When files are deleted and new files are
created, directory fragments tend to get
scattered over the entire disk
• This causes slow read/write processes
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Defragmentation can solve this issue
• Can be a lengthy process
• Would need to be performed reguraly
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Solid-State should not be defragmented
since they tend to wear down eventually
Extended
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Secondary to primary partitions
Hard disk may contain 1 extended
partition
• Can be sub-divided into logical drives
• Each are assigned additonal letter drives
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Examples
• Primary partition would be C:
• Extended partition would be E:, G: etc
Compressed Disks
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Compressed to create additional space
Creating one large file in a partition
• Storing the disk’s data in this file
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At startup, device drivers open this file
and assign it to a separate letter
To avoid confusion, the original partition
and the compressed drive had their letters
swapped
• Compressed disk would be C:
• Uncompressed disk were given higher names
Partitioning Schemes
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Microsoft
• create a single active primary partition,
the C: drive
• Where all system, user data,
applications, and page file all reside
• Some users, however, prefer to create
multiple partitions so that the operating
system can be stored separately from
other kinds of data.
Partitioning Schemes cont.
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Unix
• creation of separate partitions for /boot,
/home, /tmp, /usr, /var, /opt, swap and all
remaining files under the "/" (root directory)
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Advantages
• if one file system gets corrupted, the rest of
the data (the other file systems) stay intact,
minimizing data loss
• can be accessed read-only and the execution
of setuid files disabled thus enhancing security
• performance may be enhanced due to less disk
head travel
Partitioning Schemes cont.
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Disadvantages of Unix scheme partition
• user could run out of hard drive space in his or
her /home partition
• good implementation requires the user to
predict how much space each partition will
need, which may be a difficult task
• Logical Volume Management, often used in
servers, increases flexibility by allowing data in
volumes to expand into separate physical disks
• Another option is to resize existing partitions
when necessary.
Partition Recovery
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When a partition is deleted, generally only
the table entry is removed
The data is still on the hard disk but
maybe un-accessible
Specialized recovery tools can access the
data and recreate the table entry
Some disk utilities may also overwrite a
number of beginning sectors of a partition
they delete
In this case it may be possible to restore a
FAT32 or NTFS partition if a backup boot
sector is available